For years, activists and researchers have known that solitary confinement can destroy a person's mind, slowly stunting the growth of brain cells needed to form memories and coherent thoughts.

Many have called for reform, and this week, President Barack Obama heeded that call when he issued an executive action that will end solitary confinement for juveniles in federal prison and curtail the number of days adult prisoners can initially be placed in isolation.

Obama followed his executive action with an op-ed in The Washington Post, citing research that suggests solitary confinement could cause "devastating, lasting psychological consequences."

Here are some of the consequences inmates may face when they spend up to 23 hours per day alone in a cell.

Increased risk of suicide

Advocates of the New York City Jail Action Coalition hold a rally to call for overhauling policies concerning treatment of city jail inmates at New York's City Hall in 2014.

Image: Vanessa A. Alvarez/Associated Press

About 5% of inmates across the U.S. are held in solitary confinement, but those inmates account for approximately 50% of inmate suicides, according to psychiatrist Terry Kupers, who was in quoted in Wired in 2013.

The Department of Justice cited a 2012 study stating that half of the juvenile inmates who committed suicide were isolated when they did so, and that 62% of them had been in solitary confinement at one point.

Hallucinations and delusions

Condemned inmate Martin Navarette on death row at San Quentin State Prison in San Quentin, California, on Dec. 29, 2015.

Image: Ben Margot/Associated Press

Isolation can cause the mind to see things that aren't there and fixate on situations that don't exist, studies show.

Stuart Grassian, a former faculty member at Harvard Medical School who studied the effects of solitary confinement, once met an inmate who spent time in isolation and couldn't get rid of the feeling that his bladder was never empty. All day, he would try to alleviate himself.

Anxiety, stress and memory loss

Hinds Detention Center in Raymond, Mississippi, on June 12, 2015.

Image: Rogelio V. Solis/Associated Press

Prison isolation causes profound stress for inmates, which blocks the formation of neurons that allow for brain development and memory retention.

This is a problem for anyone in solitary confinement, but especially for people under 18 whose brains are rapidly forming and growing.

Isolation may also impact more than just memory. Evidence exists that solitary can stunt the development of brain cells that allow people to control emotions and translate thoughts into actions, too.

Lack of impulse control

Sgt. Andrew Archie walks through death row at the Georgia Diagnostic and Classification Prison, on Dec. 1, 2015, in Jackson, Georgia.

Image: David Goldman/Associated Press

Kenny, who served as a juvenile inmate in 2013, spent nearly three months of a six-month prison term in solitary confinement, during which he peed in a milk carton and hurled the contents at a guard.

In an interview with Mother Jones afterward, he seemed bewildered by his behavior. While no study has been conducted on Kenny in particular (that we know of yet), solitary confinement is thought to damage development of a part of the brain called the dorsolateral prefrontal cortex, which deals with controlling impulses and understanding consequences.

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